What is the best dose for aspirin following angioplasty: 324mg or 81mg?

General responses to selected questions from Joel Braunstein, MD, of Johns Hopkins University and Joseph Toscano, MD.


I had an angioplasty operation. My doctor prescribed 324 mg of aspirin. I read about a study that said 81 mg is a sufficient dose. Is my doctor wrong in prescribing 324 mg?


Most likely not. However, the problem with precisely answering this question in your case involves a lack of specific evidence. There seems to be no studies that look at long-term outcomes in patients after angioplasty that involve only a direct comparison of various dosages of aspirin. These studies involve variation in other medications or treatments as well, so it ends up being an "apples and oranges" comparison with respect to aspirin dosage.

To compensate, we have to apply information from studies about other groups of patients, and this is where I think confusion can arise. We find differences in optimum aspirin dosages when we consider those who have had a heart attack, those who haven't, and those who are at risk for or who have already had a stroke. (Many patients who have had a stroke end up dying of a heart attack, and to a lesser degree, vice versa.)

To add to the confusion, some very good evidence comes from Europe, where aspirin is often dosed in 100 mg increments. What's the difference between 81 mg and 100 mg or 300, 324, and 400 mg? (By the way, there is really no difference between 324 and 325 mg.)

From the information we have, we do know the following:

  1. It is absolutely clear that aspirin is effective in decreasing the chance of first and subsequent heart attacks and strokes.

  2. Aspirin adds to the benefit of angioplasty, stenting and bypass surgery to reduce the risk of heart attack after these procedures.

  3. Increasing doses of aspirin are more and more effective, though once a certain dose is reached, further increases don't seem to help more. This maximum effective dose is different for patients in different categories. For example, for those who haven't had a heart attack, there is a reduction in cardiac risk beginning at 81 mg per day, but taking 324 mg every other day works the best, on average. If a person has already had a heart attack, then 324 mg daily seems best to prevent another heart attack, and 324 mg 2-3 times a day maximally reduces the risk of stroke (though very few people actually take this much).

  1. Increasing dosages of aspirin have more potential for side effects, most notably, stomach and intestinal ulcer formation and bleeding, as well as stroke in its rarer but more severe "bleeding" form. The risk of complications increases with age. Moreover, for those at the lowest risk of a first heart attack or stroke (less than 3 percent risk), the chance of dying from a complication of aspirin may actually exceed the benefit!

So, basically, aspirin's benefits (1, 2, and 3) need to be balanced against its risks (4). Given your situation - with known, albeit treated, coronary artery disease - 81 mg daily will definitely lower your risk of heart attack and stroke. A dose of 324 mg would decrease your risk even further, but brings with it a higher chance of bleeding complications. For the "average" patient in your category, the benefit of the higher dosage probably outweighs the risk. If, however, you have uncontrolled high blood pressure (this increases the risk of bleeding stroke) or have had a stomach or intestinal ulcer in the past (this increases the risk of another ulcer), the opposite may be true.

Fortunately, each of these additional risk factors can be modified. High blood pressure can be better controlled, and ulcer risk can be reduced by acid-blocking medications. In the end, the benefit of any ongoing use of a dosage of aspirin needs to be weighed against the possible side effects in each individual patient.